Bearings for rotatably supporting the ends or mid portions of drive shafts and other types of shafts have been used for many years. Such bearings are available in a wide variety of forms for use under an equally wide variety of conditions. For example, bushings made of Teflon or other low friction plastic material are often used in situations where the shafts supported by the bearings are to be driven at relatively low rotation rates and are to bear relatively low lateral loads. To accommodate higher rotation rates and loads, bushings made of relatively soft porous metal such as bronze are often used. These types of metal bushings are advantageous over plastic bushings because they are able to bear higher lateral loads imparted by shafts and are able to accommodate higher rotation rates without overheating. In addition, porous metal bushings can be impregnated with an oil or another lubricant to reduce their coefficients of friction substantially.
In situations where high rotation rates and/or high lateral loads are to be accommodated, rolling bearings such as roller bearings and ball bearings are used. Rolling bearings offer very high lateral load bearing capability and have very low frictional resistance to accommodate much higher rotation rates than static bushings.
When rotating drive shafts are used in lighter equipment such as, for example, printers, plotters, and photocopy machines, it is common to support the shafts in bearings that are mounted in facing walls of a relatively thin metal chassis. In these circumstances, the bearings must be mounted to the walls of the chassis in such a way that they are precisely aligned with each other to receive the shaft without binding. In the past, this has been accomplished in a variety of ways. In some instances, opposing walls of the chassis are punched to form aligned holes. The bushings or bearings are then press fit into a mounting collar having mounting dogs or tabs for mounting the collar to a wall of the chassis with rivets or bolts to align the bearings with each other and with the punched holes in the chassis. While this method can work well, it is nevertheless relatively expensive because the mounting holes for the collars must be very precisely positioned for properly aligning the bearings and because several machining steps are required to mount the bearings to the walls.
Self clinching bushing assemblies have been available for securing and aligning plastic and metal bushings in opposed relatively thin sheet metal walls. U.S. Pat. No. 3,252,742 of Swanstrom discloses such a bushing assembly. The Swanstrom device includes a retainer that is adapted to be pressed into and clinch itself securely within a hole formed in a thin metal sheet. The retainer has a generally cylindrical pilot that is tapered in such a way that its narrow end can be inserted into the hole and, as the retainer is pressed further into the hole, its wide end spreads or stretches the hole slightly. A radially projecting annular head is formed at the wide end of the retainer and abuts the metal sheet when the retainer is fully pressed into the hole. An annular groove is formed in the pilot just beneath the head. When the retainer is fully pressed into the hole, the slightly stretched metal around the periphery of the hole contracts slightly into the annular groove to clinch the retainer securely in place and to align it perpendicular to the wall.
Swanstrom further discloses a plastic bushing disposed in the retainer. The bushing is formed with an outwardly projecting spherical bulge that rests against a tapered seat formed around the interior wall of the retainer and that is captured in the retainer by a crimping operation. In this way, the bushing is free to rock a bit relative to the central axis of the retainer but is nevertheless secured firmly therein. Accordingly, the plastic bushing can rock slightly as necessary to align itself precisely with a like bushing mounted in an opposing wall of the chassis for receiving and rotatably supporting a shaft.
U.S. Pat. No. 3,317,256 of Ernest discloses a similar bushing assembly wherein an lubricant impregnated packing is disposed and sealed between the retainer and a bushing mounted therein. The bushing of Ernest is made of a somewhat porous metal and thus slowly wicks lubricant from the packing through to the interface between the bushing and the shaft to provide longer term reduced friction between the bushing and the shaft. The Ernest apparatus is an attempt to accommodate higher rotation rates of the shaft than is possible with dry or impregnated bearings while still retaining the self clinching press fittable feature of the bearing assembly.
While bearing assemblies such as those disclosed in Swanstrom and Ernest have proven successful for economically installing plastic and metal bushings in relatively thin sheet metal walls, they nevertheless exhibit certain inherent shortcomings that limit their applicability. The most notable of these limitations is the inherent limitations on rotation rates and lateral load bearing capacity provided by static plastic and metal bushings. Even with lubricant impregnation and other lubricating techniques, such bushings will overheat, deform, and seize when shafts supported in them are rotated beyond a predefined limit or are subjected to substantial lateral loads. In these situations, rolling bearings must be used. However, to date there has not been available a rolling bearing assembly that can be press fit into an opening in a thin metal sheet in such a way that the assembly is self clinching and provides accurate alignment of a rolling bearing. This has been due in part to inaccurate chassis bending and punching techniques, which heretofore have not produced the tolerances required for rolling bearings, and in larger part to the failure of those skilled in the art to produce with success a functional rolling bearing assembly that exhibits self clinching press fittable characteristics. Accordingly, when rolling bearings are called for, they are still mounted in the traditional, cumbersome, and expensive way by being secured in a relatively thick bearing collar that must then be accurately mounted to the metal sheet with bolts or rivets extending through mounting dogs on the collar.
Accordingly, there exists a need for a rolling bearing assembly that offers the ease, convenience, and economy of self clinching press fittable installation in the relatively thin metal walls of an equipment chassis while at the same accurately aligning a rolling bearing rather than a static bushing for accommodating drive shafts that are to be rotated at high speeds or that are to bear high lateral loads. It is to the provision of such a rolling bearing assembly that the present invention is primarily directed.